Folding knives with a lock mechanism to keep the blade open are well known. Typically these knives have a spring actuated lock that rests either on the side of the blade or on the blade tang as the blade rotates. This positioning of the lock, and its constant contact with the blade or tang during rotation, causes friction so that blade rotation is constantly subject to drag. Also, when the blade has been in use, the strap lock interface and locking surfaces wear and the blade develops some slop or lock wiggle. This makes for a low quality knife and unsafe conditions.
A very popular design for modern folding knives is a configuration that allows for the blade to be opened by exerting pressure on a spur of the tang, protruding above the handle frame. This spur is often called a “flipper”. These knives are commonly called “Flipper Knives” and most variations rely on a locking mechanism based on the liner lock. Liner locks are well known, and an example can be found in U.S. Pat. No. 825,093 to Watson. The disadvantage of using a liner lock, in conjunction with this opening method, is that the liner lock is in continuous contact with the blade tang when the knife rotates, which generates an unacceptable level of drag on the opening blade. Folding knives of this design are difficult to open and prone to misfire, requiring an enhanced level of dexterity by the operator.
Automatic opening knives are well known in the prior art, encompassing a wide variety of features. The so-called double action configuration allows the user the option of either opening the blade in the usual automatic mode, of depressing the firing pin, or conversely, simply opening the blade with the thumb or other hand.
Most automatic opening knives are provided with a separate safety switch intended to prevent accidental firing and a very few combine the safety and the firing pin within the same button, which may be shifted in an alternate plane of motion, to engage or disengage the safety feature before firing.
The basic configuration of the blade lock, as disclosed herein, has much in common with automatic knives developed in Italy during the nineteenth century. The Italian design, herein referred to as a strap lock, relies on a flat spring affixed to the spine of the handle frame near the butt of the handle and resiliently capturing a protrusion on the blade tang to cause lock up when opened. The disadvantage of the Italian design is lack of a means to compensate for strap lock wear and it's incompatibility with modern flipper opening methods, due to the fact that the flipper spur must pass through the area occupied by the strap lock.
Prior art patents are as follows: US 462,141, U.S. Pat. No. 1,263,440, and U.S. Pat. No. 5,095,624.